An electrochemical measuring cell for detecting chlorine has become known from GB-PS 15 52 620. In the prior-art measuring cell, the measuring electrode and the counterelectrode consist of an inert material, e.g., platinum, and an electrolyte containing calcium bromide as the redox mediator is used. The redox mediator is oxidized by the chlorine to be detected at the measuring electrode, and the bromine formed in the process can be again reduced into Br.sup.- at the inert measuring electrode. However, it was found that the bromine formed during the oxidation of chlorine is not completely reacted at the measuring electrode, but it enters the electrolyte space and leads to memory effects. Bromine is formed from the bromide ions at the counterelectrode, and this bromine leads to the above-mentioned memory effects, on the one hand, and it interferes with the measuring electrode, on the other hand. The presence of bromine in the electrolyte leads to long rise and decay times of the measured signal, and no stable plateau value develops in the case of continuous exposure to chlorine.